Compounds of formulas A to E ##STR1## are described as dopamine agonists in U.S. Pat. Nos. 4,552,956, 4,537,893, 4,198,415, 4,501,890 and European Patent Application No. 172,697 respectively.
Compounds of formula F ##STR2## are described as hypotensive agents in U.S. Pat. No. 4,596,871.
An object of the present invention was to find a dopamine agonist having selectivity for the presynaptic dopamine receptor, i.e. an autoreceptor. The advantage of an autoreceptor agonist is that it modulates the activity of dopaminergic systems selectively, without the postsynaptic stimulation which is inherent to nonselective dopamine agonists.